To start off i'm a diesel mechanic, I build engines so I'm a bit more knowledgeable than a do it your selfer. I recently put a true trac diff and 3.73 gear set in my 2005 v6 mustang, and had no noises for the first hundred miles. I'm at about 250 miles now, and I get a whine when I'm barely on the throttle. on the throttle, silent, engine braking silent, barely on the throttle enough to take load off the rear end, and it whines a little. After breakin I started beating on it, no issues, seems happy and healthy aside from that occasional whine. Next weekend I figure i'll open it up and look for wear, just looking for some opinions until then.